Aircraft arresting gear

ABSTRACT

The invention consists in an aircraft arresting gear wherein a rope or net is stretched across a runway and is secured to power absorbing means located at each side of the runway. Connected to each end of the rope or net is a belt having transverse teeth. Each belt is passed through a casing having inlet and outlet ports. Hydraulic fluid introduced through an inlet port fills the gaps between the teeth as the belt passes through the casing and means are provided by which such fluid is displaced and discharged through the outlet port under pressure. Such means may be in the form of a tooth wheel which meshes with the teeth of the belt. The discharged fluid passes through a valve by which the outlet pressure can be controlled to regulate the retarding force applied to the belt. Such control regulates the retarding force applied to the aircraft being arrested.

United States Patent n 1 Matthew [54] AIRCRAFT ARRESTING GEAR [75]Inventor: John Campbell Matthew, Lasswade,

Scotland [73] Assignee: Mactaggart,

Limited [22] Filed: March 2, 1971 [21] App]. No.: 120,195

Scott 8: Company,

[52] U.S. Cl. ..244/ll0 A, 188/290 [5i] Int. Cl. ..B64f l/02 [58] Fieldof Search ..244/1l0, 63; 188/292, 290

[56] References Cited UNITED STATES PATENTS 3,200,906 8/1965 Bernard..244/1 10 A 3,352,516 1l/l967 Jackson ..244/l l0 A 3,481,565 12/l969Marcheron ..244/l 10 A Primary ExaminerMilton Buchler AssistantExaminerPaul E. Sauberer Att0rneyHolman & Stern 51 Jan. 30, 1973 [57]ABSTRACT The invention consists in an aircraft arresting gear wherein arope or net is stretched across a runway and is secured to powerabsorbing means located at each side of the runway.

Connected to each end of the rope or net is a belthaving transverseteeth. Each belt is passed through a casing having inlet and outletports. Hydraulic fluid introduced through an inlet port fills the gapsbetween the teeth as the belt passes through the casing and means areprovided by which such fluid is displaced and discharged through theoutlet port under pressure. Such means may be in the form of a toothwheel which meshes with the teeth of the belt. The discharged fluidpasses through a valve by which the outlet pressure can be controlled toregulate the retarding force applied to the belt. Such control regulatesthe retarding force applied to the aircraft being arrested.

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AIRCRAFT ARRESTING GEAR This invention has reference to aircraftarresting gear for retarding the motion of aircraft after landing incircumstances when the length of the runway available for bringing theaircraft to rest is limited. The invention relates particularly to thatkind of arresting gear which consists of a rope span or net, stretchedtransversely across the runway, which is engaged by the aircraft or by ahook attached to the aircraft, the rope or ropes attached to the netbeing led over guide pulleys on each side of the runway and thence topower absorbing means which, when the rope or net is engaged by anaircraft, control the rope or net tension while the aircraft is beingarrested.

According to the present invention in an arresting gear of the kind setforth each end of the rope or net is connected to power absorbing meanscomprising a flexible belt having transversely extending teeth on atleast one face thereof, a casing having inlet and outlet ports andthrough which the belt passes, means provided with teeth which mesh withthe gaps between the teeth of the flexible belt and by which hydraulicfluid introduced through the inlet port into the gaps between the teethof the belt is thereafter pumped through the outlet port and valve meansto regulate the back pressure of the pumped fluid and thereby theretarding force of the arresting gear.

Each belt may have transverse teeth on both faces thereof and the casingprovided with two inlet ports, two outlet ports and two toothed wheels,one meshing with the teeth on one face of the belt and the other withthe teeth on the other face of the belt, the belt and toothed wheelsthereby forming two gear pumps with a casing common to both.

The casing may have a series of alternate inlet and outlet ports on oneside of the belt, a corresponding series of inlet and outlet ports onthe other side of the belt and a toothed wheel between each pair ofinletand outlet ports.

The invention also consists in an arresting gear as set forth in thepreceding paragraph but two wherein each end of the rope or net isconnected to two superimposed belts having intermeshing teeth on theiropposed faces, the superimposed belts being passed through the casingwhich incorporates guide means by which the belts, during their traversethrough the casing, are separated and thereafter forced together, theseparating of the belts permitting hydraulic fluid to enter between thebelts through the inlet port while the subsequent meshing of the teethforces the trapped fluid through the outlet port.

The invention further consists in an arresting gear as set forth in anyof the four preceding paragraphs in combination with an accumulatorconnected to the outlet ports and which is charged through a non-returnresetting valve when the belt is drawn through the casing by theaircraft being retarded, the said pump functioning as a motor powered bythe accumulator when the valve is reset so that the pump will retractthe belt.

The teeth of the belts may be protected by the teeth of protective beltsmeshing therewith, guide means being provided whereby the protectivebelts are separated from the first mentioned belts when the latter arepassing through the casing containing the toothed wheel and furtherguide means provided to thereafter cause said teeth to again intermeshwith the teeth of the first mentioned belts.

In an alternative arrangement each belt connected to the rope or net isa composite belt formed of two belts having teeth on only one facethereof, the two belts being back to back with their teeth outwards whenfed to and drawn through the casing so that their teeth mesh with thetoothed wheels therein, guide means being provided by which the beltsforming each composite belt are separated to form two U-loops afterleaving the casing and further guide means by which the teeth of the twobelts are thereafter caused to mesh to form the composite belt.

In a further embodiment of the invention each power absorbing meanscomprises a hydraulic gear type pump casing, pairs of opposed gearwheels located within the casing, two parallel endless belts associatedwith the casing and arranged back to back, the inner faces of each belthaving transversely extending teeth, guide rollers around which thebelts are passed, the opposed runs of the belts passing through thecasing and between the opposed gear wheels so that their transverselyextending teeth mesh with the gaps between the teeth of the pump gearwheels, and a cable sandwiched between the opposed runs of the belts andconnected at one of its ends to the adjacent end of the aircraftengaging means, the cable when pulled by the aircraft engaging meansdriving the endless belts. The outer faces of the endless belts arepreferably formed of resilient material.

Reference will now be made to the accompanying drawings wherein:

FIG. 1 is a diagrammatic perspective view of one embodiment of theinvention;

FIG. 2 is a diagrammatic sectional elevation of the power absorbingmeans;

FIG. 3 shows diagrammatically to a larger scale a sectional view of thepower absorbing means;

FIG. 4 shows diagrammatically an alternative construction of powerabsorbing means;

FIG. 5 shows the provision of further belts with transverse teeth toprotect the teeth of the belts which mesh with the toothed wheels;

FIG. 6 is a diagrammatic perspective view showing the power absorbingmeans with composite belt and guiding means therefor;

FIG. 7 is a diagrammatic perspective view of a further embodiment of theinvention;

FIG. 8 is a sectional elevation of part of the power absorbing means.

FIG. 9 is a plan view, partly in section, of a further construction ofpower absorbing means for the aircraft arresting gear, and

FIGS. 10,11 and 12 are sections on the lines 10-10, 1ll1 and 12-12respectively of FIG. 9.

As shown in FIG. 1 the improved aircraft arresting gear includes a ropeor net 10 which is stretched transversely across the runway and which atthe ends thereof is connected to belts 11 and 12. Both belts areprovided with transversely extending teeth 13 on each face thereof. Eachbelt passes over a guide pulley 14a and through a pump casing 14 in eachof which are pairs of toothed wheels 15 and 16, see FIG. 3, the toothedwheels 15 mating with the teeth 13 on one face of the belt and thetoothed wheels 16 mating with the teeth on the other face of the belt.Each casing has inlet ports 17 and outlet or delivery ports 19, therebeing an inlet port at one side of each toothed wheel and an outlet portat the other side of each toothed wheel. Between each inlet and outletport the casing is such that the toothed wheels make wiping contacttherewith. Thus each toothed wheel with its casing and the beltconstitute a gear type pump. There may be any number of such pumps.

In the construction shown diagrammatically in FIG. 2 there are fourpumps, each designated 18, on each side of the belt, the inlet andoutlet ports of opposite pumps being interconnected so that the tendencyof difference in pressure in the opposite pumps bending the belt isavoided. The delivery of each pump passes through a control valve 24 bywhich the delivery pressure and hence the back pressure or retardingforce applied to the belt can be regulated.

The pumps may be connected in series and/or in parallel.

The inlet to each series of pumps on opposite sides of the belt is shownconnected to inlet pipe 21 see HO. 2 and the outlet of each series isconnected to an outlet pipe 22, the latter being connected through acooler 23 to the inlet pipe.

lt will be seen that each series of pumps of each power absorber has aclosed fluid circuit and that part of the circuit together with thecooler is common to the series on both sides of the belt. The commonpart of the circuit is connected to a make-up tank or reservoir 24a.

Normally the two belts 11 and 12 are in the main stowed concertina-wisein bins 25.

Located between each bin and the first of each series of gear type pumps18 are further gear type pumps 32 which also function as motors whenresetting as later described.

Each pump 32 has ports connected through a common pipe line and anon-return resetting valve 33 with an accumulator 34 and has furtherports connected through a pipe line 35 with the make-up tank orreservoir 24a.

Within the casing 14 at one end thereof are sealing rotors 48 and withinthe casing at the other end thereof are similar sealing rotors 49. Eachof said sealing rotors have teeth with which mesh the teeth of the beltpassing through the casing.

The sealing rotors are of the same construction as and operate in likemanner to the toothed wheels of the pumps and serve to maintain asubstantially closed hydraulic circuit by reducing leakage.

Each sealing rotor when rotated in one direction discharges through anon-return valve 50 into the hydraulic system and any leakage past thesealing rotors is discharged into a leakage tank 51. Thus when the beltis drawn to the right as viewed in FIG. 1 the fluid carried in the beltteeth gaps is pumped back to the hydraulic system by the sealing rotors48 through the non-return valves 50. Any fluid which does leak past therotor seal is collected in its leakage tank 51. Meantime the returnvalves at the other end of the casing prevent the pressure fluid passingto the sealing rotors 49.

When the belt is moved to the left the sealing rotors 49 now act in likemanner to that of the sealing rotors 48 above described.

When an aircraft lands and engages the rope or net 10 the two belts 11and 12 are thereby pulled through their pump casings 14. Hydraulic fluidtrapped between the teeth of the belt is thereby forced through theoutlet ports 19 and through the cooler to be re-cycled through the inletports 17. The resistance offered to the fluid being pumped acts as abraking force on the rope to arrest the aircraft. The braking force canbe controlled by throttling pumped fluid by means of the valves 24.

When the belts are pulled through the pump casings each is also pulledthrough the casings of the two pumps 32 each of which draws hydraulicfluid from the tank or'reservoir 24a and forces said fluid underpressure past the non-return valve 33 into the accumulator 34 which isthereby charged. After the aircraft has been arrested said resettingvalves are opened so that pressure fluid is supplied to the pumps 32which now function as motors and feed back the belts into the bins sothat the gear is now prepared to arrest a further aircraft.

in another embodiment of the invention each end of the rope or net 10 isconnected to a pair of belts 11a and 12a having intermeshing transverseteeth 13a, see PK). 4. Each pair of belts is normally stowed in a binand is passed through an elongated casing formed by an upper guide bar25, a lower guide bar 26 and sidecover plates 27 and 28, the beltspassing between the guide bars. Within the casing is a series of fixedseparating blocks 29 each of which is of sinusoidal formation. Near oneend of each block is an inlet port 30 and near the other end of eachblock is an outlet port 31. There are gaps formed between the belts ateach end of the separating blocks, alternate gaps being connected to theports 30 and 31.

These gaps between the guide bars extend from end to end of the casingand are of such dimensions that the superimposed belts lla and 12a makea sliding fit therein. I

The inlet and outlet ports are interconnected with control valves,cooler, etc., as in the previously described embodiment of theinvention.

When the superimposed belts are drawn through the casings, which willoccur when the rope or net is engaged by the aircraft, hydraulic fluidfed through the inlet ports 30 fills the gaps between the teeth of thebelts and is carried thereby over the under the blocks 29. When theteeth again mesh the trapped fluid is forced through the outlet ports31. Thus the belts, the casing and the separating blocks act like aseries of gear pumps and by reason of the resistance offered to the flowof the fluid a braking force is applied to the belts and this in turndecellerates the aircraft.

In FIG. 5 each power absorber of the arresting gear has a belt 11 withtransverse teeth on both faces thereof. To protect said teeth twoadditional belts are provided, said belts, which are designated 36 and37, have transverse teeth 38 on their opposed faces which mesh with theteeth of the belt 11. That is, the belt 11 is sandwiched between thebelts 36 and 37, their teeth intermeshing. Before the belt 11 enters thecasing the belts 36 and 37 are separated therefrom, one of the belts 36being then guided over the pump casing and the other belt 1 l is guidedbelow the pump casing.

At the other end of the casing the belts 36 and 37 are guided by rollersso that their teeth again mesh with those of the belt 11. Thus, exceptwhere the belt 11 is approaching, passing through and leaving the casingits teeth are protected by the belts 36 and 37 between which it issandwiched.

Where the belt 11 or 12 has teeth on only one face thereof it will beunderstood that only one additional belt is required to protect theteeth thereof.

in the arrangement shown in FIG. 6 each belt attached to a rope or netis a composite belt formed of two belts 39 and 40 each having transverseteeth 41 on one face. Where the composite belt is stowed in the bin andwhere it extends to and through the casing 14 the two belts are back toback with their teeth outwards. The teeth thus mesh with the toothedwheels within the casing as described with reference to FIGS. 1, 2 and3.

When the composite belt emerges from the casing the two belts 39 and 40pass around the two guide toothed wheels 42 and 43 to form U loops, thenpass over further toothed wheels 44 and 45 and then between guiderollers 46 and 47 by which the teeth of the opposed belts are caused tointermesh to form the composite belt which is attached to one end of therope or net. Thus the teeth of the composite belt, where it extends fromthe rollers to the rope or net, are protected.

When the composite belts are retracted each is separated by the toothedwheels 44 and 45 and brought back to back by the toothed wheels 42 and43 to pass through the casing 14 to be stowed in a bin.

The embodiment of the invention shown in FIGS. 7 and 8 is substantiallysimilar to the embodiment of the invention shown diagrammatically inFIG. 2 and differs therefrom only in the construction of the belts andthe means whereby they are drawn through the pump casings. Consequentlyonly such parts of the arresting gear need now be particularlydescribed, the other parts thereof bearing the same reference numeralsas the corresponding parts shown in FIG. 2.

The two ends of the rope or net are respectively connected to cables 51and 52. Associated with each pump casing 14 are two endless belts 59 and60 each having on its inner face transversely extending teeth 61 andeach being passed around rollers 62 and 63 at the ends of the adjacentcasing and exterior thereto. The inner runs of the belts 59 and 60 areback to back and pass longitudinally through their associated casingfrom end to end. The teeth of the belts and the teeth of the gear wheelsinter-mesh to form a series of gear type pumps. As previously describedthe outlet of each pump passes through a control valve by which thedelivery pressure can be regulated and hence the retarding force appliedto the belts.

The outer faces of the belts are of rubber or other suitable resilientmaterial and sandwiched between the two belts 59 and 60 of one of thepower absorbers is the cable 51 and sandwiched between the belts of theother power absorber is the cable 52. Each of said cables passes over aguide pulley 66 to be stowed in a receptacle 67.

It will be appreciated that the cables are frictionally gripped byopposed runs of the endless belts, the grip being due, at least in partto the pressure of the fluid in the high pressure side of each pump,said pressure acting on the belts.

When an aircraft lands on the runway and engages the rope or net the twocables or flexible members drive the endless belts so that hydraulicfluid trapped between their teeth is forced by the teeth of the wheelsthrough the outlets. As the outlets are controlled by valves thepressure of the fluid ejected therethrough can be regulated to give therequired retarding force to the travel of the endless belts andtherefore to the retarding force exerted by the rope of net on theaircraft.

It will be appreciated that the lengths of the belts are substantiallyshorter than those provided in the first described embodiment of theinvention.

As shown in FIG. 9 the power absorber comprises a series of powerabsorbing units connected end to end. FIG. 9 shows three unitsdesignated 70, 71a and 70b but it will be understood that there may beany number of units. The units have end flanges 71 which are boltedtogether.

Each unit comprises an inner section 72, an upper section 73 and a lowersection 74. In FIG. 9 the inner section 72 of the unit 70 is shown insection and the upper section 73 of the unit 70a is likewise shown insection.

The inner section of each unit has top and bottom side plates betweenwhich extend a pair of tubular bearings 76 and 76a and a second pair ofbearings 77 and 770.

On the bearings 76 and 77 are rotatably mounted gear wheels 80 and 81over which is trained an endless belt 82 having on its inner facetransverse ribs or teeth 82a which mesh with the gaps between the teethof the said gear wheels. On the bearings 76a and 770 are rotatablymounted gear wheels 83 and 84 over which is trained an endless belt 85likewise having transverse ribs or teeth 85a which mesh with the gapbetween the teeth of the gear wheels 83 and 84. Between the op posedfaces of the two belts of successive units is sandwiched a cable 86which at one end thereof is attached to one end of the rope or net whichspans the runway and at the other end thereofis stowed in a bin.

It will be understood that this power absorber is positioned at one sideof the runway and that a second similar power absorber is positioned atthe other side of the runway, the cable of the second power absorberbeing attached to the other end of said rope or net.

Extending between the two gear wheels 80 and 81 is a pump body member 87which at the ends thereof is of concave formation so that the gearwheels 80 and 81 make wiping contact therewith. Extending between thegear wheels 83 and 84 is a pump body member 88 likewise of concaveformation at both ends thereof to make wiping contact with the gearwheels 83 and 84.

Each of said pump body members has a high pressure duct 89 whichconstitutes an outlet port communicating with a chamber 89a at the innerrun ofthe adjacent belt and adjacent gear wheel and has also a lowpressure passage 90 which constitutes an inlet port with branches 90aand 90b the former terminating at the adjacent gear wheel and the latterterminating at the inner run of the adjacent belt near to the gear wheel81 or 84.

In each upper section 73 is a high pressure valve chamber 91 which is incommunication with one end of the high pressure chamber 89, the otherend of which is closed and which encircles an axially sliding hollowcylindrical valve member 91a having a multiplicity of perforations. Thevalve member has an external screw thread at one end thereof which isscrewed within a cylindrical low pressure chamber 92. At the other endof said valve member is an opening of square section in which fits a key93 of similar section, the key forming the end of a spindle 93a on whichis a worm wheel 93b which incorporates a torque limiting device 94a suchas a slipping clutch. The worm wheel is rotated by means of a worm 94fast on a spindle 95 the inner end of which is keyed to the gear wheel81. The valve thus moves in unison with the belts within the limits ofits travel. lf the-belts over travel the valve,=the"sl-ipping clutch 94acomes into action.

The low pressure chamber 92 communicates with one end of each of thetubular bearings 76 and 76a the other ends of which are in communicationwith a low pressure fluid chamber 96 and 97 in the lower section 74 ofeach unit.

The said pump body members 87 and 88 form cavities 98 and 99 closed bythe outer runs of the two belts which cavities drain into cavities 100in the lower section of each unit.

in describing the operation of one of said units it will be assumed thatit is fully charged with hydraulic fluid, that an aircraft has alightedon the runway and the cable 86 is drawn therethrough from right to leftas viewed in FIG. 9. The cable then drives the two belts 82 and 85between which it is tightly sandwiched and the belts in turn rotate thegear wheels. The fluid carried around by the two gear wheels 80 and 83is displaced by the teeth or ribs of the belts 82 and 85 and is forcedunder pressure into the high pressure chambers 89. Such fluid encountersthe valve member and the resistance offered by the valves to the passageof fluid thereto determines the pressure of fluid and therefore the backpressure offered thereby to the travel of the belts and therefore theretarding force applied by the belts to the cable. The greater suchforce the greater is the retarding force applied to the aircraft.

As the aircraft is being thus retarded the worm and worm-wheel gearingshifts the valve member so that more and more of its perforations areblanked off to increase the retarding effect.

The fluid in the receptacles 98 and 99 fills the gaps between the teethof the belts and this fluid is maintained under pressure by beingdisplaced by the teeth of the gear wheels.

What l claim is:

1. An arresting gear for arresting the motion of an aircraft landing ona runway comprising aircraft engaging means stretched across the runway,power absorbing means located at each side of the runway, each powerabsorbing means comprising at least one flexible belt havingtransversely extending teeth, a casing through which the belt extendsand through which the belt is pulled by the aircraft engaging means whenan aircraft engages therewith the casing having an inlet port and anoutlet port, means by which the hydraulic fluid is fed to the inlet portto fill the gaps between said teeth. means by which the fluid in saidgaps is discharged through the outlet port and valve means by which thepressure of the discharged fluid can be controlled so that the backpressure exerted on the flexible belt can be regulated to control theretarding of the aircraft.

2. An arresting gear as claimed in claim 1 wherein each power absorbingmeans is provided with a toothed gear which meshes with the teeth of thebelt passing therethrough to form a pump so that the hydraulic fluid inthe gaps between the teeth of the belt is discharged under pressurethrough the outlet.

3. An arresting gear as claimed in claim 1 wherein each belt hastransverse teeth on both faces thereof and the casing through which itpasses is provided with two inlet ports, two outlet ports and twotoothed wheels, the teeth of one wheel meshing with the gaps between theteeth on one face of the belt and the teeth of the other wheel meshingwith the gaps between the teeth on the other face of the belt, the beltand tooth wheels thereby forming two gear type pumps with a casingcommon to both.

4. An arresting gear as claimed in claim 2 wherein the casing of eachpower absorbing means has a series of alternate inlet and outlet portson one side of the belt, a corresponding series of inlet and outletports on the other side of the belt and a tooth wheel between each pairof inlet and outlet ports.

5. An arresting gear as claimed in claim 1 wherein each end of theaircraft engaging means is connected to two superimposed belts havingintermeshing teeth on their superimposed faces and which extend throughthe casing, guide means by which the belts during their traverse througheach casing are separated and thereafter forced together, the separatingof the belts permitting the hydraulic fluid to enter between the beltsthrough the inlet port while the subsequent meashing of the teeth andgaps forces the fluid trapped in the gaps through the outlet port.

6. An arresting gear as claimed in claim 2 wherein each power absorberhas an accumulator connected to the outlet port and a non-returnresetting valve introduced between each accumulator and outlet port andthrough which hydraulic fluid is forced by a toothed wheel when the beltis drawn through its casing, the said wheels functioning as motorspowered by the accumulators when the valves are reset so that theyretract the belt.

7. An arresting gear as claimed in claim 2 wherein the teeth of the beltof each power absorbing means are protected by a protective belt havingteeth which mesh with the teeth of the first-mentioned belt, each powerabsorbing means having guide means which separate the intermeshing beltswhen passing through its casing and further guide means to thereaftercause the teeth of the belts to intermesh.

8. An arresting gear as claimed in claim 2 wherein the belt of eachpower absorbing means is a composite belt formed of two belts eachhaving teeth on one face only, the belts being back to back with theirteeth outwards when fed to and drawn through the casing and whereinguide means are provided by which the belts forming each composite beltare separated to form two U loops after leaving the casing and furtherguide means by which the teeth of the two belts forming the compositebelt are forced together after passing through the casing.

9. An arresting gear for arresting the motion of an aircraft landing ona runway as claimed in claim 1 wherein each power absorbing meanscomprises a hydraulic gear type pump casing having inlet and outletports, pairs of opposed pump gear wheels rotatably mounted within thecasing, two parallel endless belts arranged back to back with theiropposed runs extending through the casing and between the opposed gearwheels, the inner faces of the belts having transversely extending teethwhich mesh with the pump gear wheels, means by which hydraulic fluidunder pressure is supplied to the inlet ports of the casing, valve meansby which the pressure of fluid discharged through the outlet ports iscontrolled and flexible means sandwiched between the opposed runs of thetwo belts and secured to the means extending across the runway, thearrangement and construction being such that when the means stretchedacross the runway is engaged by an aircraft the flexible means connectedthereto are pulled through the casings and the gear wheels are rotatedso that hydraulic fluid carried round by the gear wheels is dischargedunder pressure by the ribs of the belts, the resistance encountered bythe gear wheels due to the controlled pressure of the discharged fluidbeing transmitted through the belts to the aircraft engaging means whichtransmits a retarding force to the aircraft.

10. An arresting gear as claimed in claim 9 wherein the outer faces ofthe endless belts are of resilient material.

11. An arresting gear as claimed in claim 9 wherein each power absorbingmeans is formed of a series of units each of which is formed of threesections, namely an inner section carrying pairs of rollers over whichthe endless belts are trained, a second section having valve meansactuated by the belts and by which the retarding force of the fluiddischarged by gear wheels is controlled, and a third section providingpart of the hydraulic flow system by which fluid is supplied to the gearwheels.

12. An arresting gear as claimed in claim 9 wherein the belts are formedof resilient material and wherein high pressure fluid acts on the beltsto ensure that the flexible members are tightly sandwiched between theopposed runs of the belts.

1. An arresting gear for arresting the motion of an aircraft landing ona runway comprising aircraft engaging means stretched across the runway,power absorbing means located at each side of the runway, each powerabsorbing means comprising at least one flexible belt havingtransversely extending teeth, a casing through which the belt extendsand through which the belt is pulled by the aircraft engaging means whenan aircraft engages therewith the casinG having an inlet port and anoutlet port, means by which the hydraulic fluid is fed to the inlet portto fill the gaps between said teeth, means by which the fluid in saidgaps is discharged through the outlet port and valve means by which thepressure of the discharged fluid can be controlled so that the backpressure exerted on the flexible belt can be regulated to control theretarding of the aircraft.
 1. An arresting gear for arresting the motionof an aircraft landing on a runway comprising aircraft engaging meansstretched across the runway, power absorbing means located at each sideof the runway, each power absorbing means comprising at least oneflexible belt having transversely extending teeth, a casing throughwhich the belt extends and through which the belt is pulled by theaircraft engaging means when an aircraft engages therewith the casinGhaving an inlet port and an outlet port, means by which the hydraulicfluid is fed to the inlet port to fill the gaps between said teeth,means by which the fluid in said gaps is discharged through the outletport and valve means by which the pressure of the discharged fluid canbe controlled so that the back pressure exerted on the flexible belt canbe regulated to control the retarding of the aircraft.
 2. An arrestinggear as claimed in claim 1 wherein each power absorbing means isprovided with a toothed gear which meshes with the teeth of the beltpassing therethrough to form a pump so that the hydraulic fluid in thegaps between the teeth of the belt is discharged under pressure throughthe outlet.
 3. An arresting gear as claimed in claim 1 wherein each belthas transverse teeth on both faces thereof and the casing through whichit passes is provided with two inlet ports, two outlet ports and twotoothed wheels, the teeth of one wheel meshing with the gaps between theteeth on one face of the belt and the teeth of the other wheel meshingwith the gaps between the teeth on the other face of the belt, the beltand tooth wheels thereby forming two gear type pumps with a casingcommon to both.
 4. An arresting gear as claimed in claim 2 wherein thecasing of each power absorbing means has a series of alternate inlet andoutlet ports on one side of the belt, a corresponding series of inletand outlet ports on the other side of the belt and a tooth wheel betweeneach pair of inlet and outlet ports.
 5. An arresting gear as claimed inclaim 1 wherein each end of the aircraft engaging means is connected totwo superimposed belts having intermeshing teeth on their superimposedfaces and which extend through the casing, guide means by which thebelts during their traverse through each casing are separated andthereafter forced together, the separating of the belts permitting thehydraulic fluid to enter between the belts through the inlet port whilethe subsequent meashing of the teeth and gaps forces the fluid trappedin the gaps through the outlet port.
 6. An arresting gear as claimed inclaim 2 wherein each power absorber has an accumulator connected to theoutlet port and a non-return resetting valve introduced between eachaccumulator and outlet port and through which hydraulic fluid is forcedby a toothed wheel when the belt is drawn through its casing, the saidwheels functioning as motors powered by the accumulators when the valvesare reset so that they retract the belt.
 7. An arresting gear as claimedin claim 2 wherein the teeth of the belt of each power absorbing meansare protected by a protective belt having teeth which mesh with theteeth of the first-mentioned belt, each power absorbing means havingguide means which separate the intermeshing belts when passing throughits casing and further guide means to thereafter cause the teeth of thebelts to intermesh.
 8. An arresting gear as claimed in claim 2 whereinthe belt of each power absorbing means is a composite belt formed of twobelts each having teeth on one face only, the belts being back to backwith their teeth outwards when fed to and drawn through the casing andwherein guide means are provided by which the belts forming eachcomposite belt are separated to form two U loops after leaving thecasing and further guide means by which the teeth of the two beltsforming the composite belt are forced together after passing through thecasing.
 9. An arresting gear for arresting the motion of an aircraftlanding on a runway as claimed in claim 1 wherein each power absorbingmeans comprises a hydraulic gear type pump casing having inlet andoutlet ports, pairs of opposed pump gear wheels rotatably mounted withinthe casing, two parallel endless belts arranged back to back with theiropposed runs extending through the casing and between the opposed gearwheels, the inner faces of the belts having transversely extending teethwhich mesh with the pump gear wheels, means by which hydraulic fluidundeR pressure is supplied to the inlet ports of the casing, valve meansby which the pressure of fluid discharged through the outlet ports iscontrolled and flexible means sandwiched between the opposed runs of thetwo belts and secured to the means extending across the runway, thearrangement and construction being such that when the means stretchedacross the runway is engaged by an aircraft the flexible means connectedthereto are pulled through the casings and the gear wheels are rotatedso that hydraulic fluid carried round by the gear wheels is dischargedunder pressure by the ribs of the belts, the resistance encountered bythe gear wheels due to the controlled pressure of the discharged fluidbeing transmitted through the belts to the aircraft engaging means whichtransmits a retarding force to the aircraft.
 10. An arresting gear asclaimed in claim 9 wherein the outer faces of the endless belts are ofresilient material.
 11. An arresting gear as claimed in claim 9 whereineach power absorbing means is formed of a series of units each of whichis formed of three sections, namely an inner section carrying pairs ofrollers over which the endless belts are trained, a second sectionhaving valve means actuated by the belts and by which the retardingforce of the fluid discharged by gear wheels is controlled, and a thirdsection providing part of the hydraulic flow system by which fluid issupplied to the gear wheels.